In the conventional art, the seal ring of this kind is used in a variety of hydraulic apparatus such as an automatic transmission for an automobile.
A general seal ring will be described with reference to FIG. 11 and FIG. 12. FIG. 11 is a perspective view showing the mounted state of a seal ring according to the conventional art. FIG. 12 is a schematic section showing the mounted state of the seal ring according to the conventional art.
The shown seal ring 100 seals the annular clearance between a housing 800 that has a bore and a shaft 700 inserted in the bore. This seal ring 100 is mounted for use in an annular groove 701 formed in the shaft 700.
The seal ring 100 is made of a resin material. The seal ring 100 is provided with a first sealing face 100a for sealing the inner circumference 800a of the bore formed in the housing 800, and a second sealing face 100b for sealing the side wall face 701a of the annular groove 701 formed in the shaft 700.
When a pressure is applied in the direction of arrow P, as shown, from the sealing fluid to the unsealing fluid, the seal ring 100 is pushed to the side of the unsealing fluid. Therefore, the second sealing face 100b pushes the side wall face 701a of the annular groove 701. On the other hand, the first sealing face 100a pushes the inner circumference 800a of the bore confronting the annular groove 701. Thus, the first sealing face 100a and the second sealing face 100b seal at their respective positions.
Therefore, the seal ring 100 can prevent the sealing fluid from leaking to the side of the unsealing fluid.
Here, the sealing fluid is exemplified by lubricating oil, and indicates the ATF (Automatic Transmission Fluid) in case it is used in the transmission of an automobile.
On the other hand, the ring body of the seal ring 100 is provided with a separate portion 101 at one circumferential portion, as shown. One reason for this provision is to facilitate the work for mounting the seal ring 100 in position.
A variety of types have been known as that mode of the separate portion 101. The example shown in FIG. 11 and FIG. 12 is a special step cut. This special step cut has a construction cut into two steps. By adopting this special step cut, the leakage can be reduced to properly match the change in the ambient temperature.
This special step cut is provided with a pair of a projection 101a and a depression 101d on one outer circumferential side across the separated portion and a pair of a depression 101c and a projection 101b on the other outer circumferential side. The construction is further made such that the projection 101a and the depression 101c fit each other whereas the depression 101d and the projection 101b fit each other.
The seal ring 100 adopting such special step cut can block the sealing fluid side and the unsealing fluid side such that the faces perpendicular to the circumferential direction form clearances with respect to the circumferential direction. As a result, even if the ring body is expanded or contracted by the ambient temperature, the seal ring 100 can absorb the changes in the sizes of the clearances while keeping the sealed state. As a result, the seal ring 100 can keep its sealing properties stably against the surrounding temperature change.
In recent years, the various hydraulic apparatus such as the automatic transmission for the automobile has needs of not only the leakage reduction but also the reduction of the friction of the sliding rotations for the seal ring used in the automatic transmission with a view to improving the fuel economy and the performance.
As shown in FIG. 13 and FIG. 14, therefore, there is known a structure which is reduced in the pressure receiving area of the sealing faces. FIG. 13 is a perspective view showing the mounted state of the seal ring according to the conventional art. FIG. 14 is a schematic section showing the mounted state of the seal ring according to the conventional art. The seal ring, as shown in these Figures, according to the conventional art is constructed to reduce the friction of the sliding rotations from that of the seal ring according to the conventional art as shown in FIG. 11 and FIG. 12.
This seal ring 200 is provided, like the aforementioned seal ring 100, with a first sealing face 200a, a second sealing face 200b, and a separate portion 201 having a special step cut (including a projection 201a, a depression 201d, a depression 201c and a projection 201b).
In order to reduce the pressure receiving area (or the sliding area) on the sidewall face 701a of the annular groove 701, moreover, this seal ring 200 is provided with a relief (as can also be called the “depression”, “notch” or “recess”).
Thus, this seal ring 200 contemplates to reduce the friction of the sliding rotations by reducing the pressure receiving area.
In case the side wall face 701a of the annular groove 701 is perpendicular to the groove bottom (that is, in case the second sealing faces 100b and 200b and the side wall face 701a are parallel to each other), the aforementioned seal rings 100 and 200 seal throughout their circumferences. Therefore, the problem of the leak does not arise.
However, the annular groove 701 may have its side wall face sloped such that its bottom is narrow and such that it becomes the wider as it comes the closer to its upper face. Generally, the slope occurs when the annular groove 701 is formed by the cutting work. In this case, there arises a problem that the sealing performance is not done throughout the circumference of the seal ring so that the leakage increases. This point will be described with reference to FIG. 15 to FIG. 18.
The case of the aforementioned seal ring 100 is shown in FIG. 15 and FIG. 16. In case the side wall face 702a of an annular groove 702 is sloped, as shown, a sealing portion S is formed of only the lower end of the seal ring 100. In short, the sealing action is performed in a substantially linear contact.
The reason for the expression of not merely the “linear contact” but the “substantially linear contact” is described in the following. This is because the contact is practically made through a face having a small width so that it is so grasped rather by the facial contact but not by the linear contact as to invite a misunderstanding. This expression also applies to the following description.
A clearance X usually exists in the seal ring 100 adopting the special step cut at the separate portion 101, as shown.
This is because the seal ring 100 adopting the special step cut is constructed such that the clearance is formed between the faces perpendicular to the circumferential direction so as to correspond to the change in the ambient temperature.
In case the sealing action is performed by the substantially linear contact in the sealing portion S, as described above, it is apparent from the FIGS that an unsealed portion arises in the clearance X. Therefore, a leak occurs (at a leaking portion A).
On the other hand, the case of the aforementioned seal ring 200 is shown in FIG. 17 and FIG. 18.
In this case, the sealing portion S is formed at the lower end of the seal ring 200 in the portion having no relief 202 and at the step portion over the relief in the portion having the relief 202, as shown. In this case, too, the leak occurs (at leaking portion A) from the clearance X as in the case of the aforementioned seal ring 100.
In the case of this seal ring 200, on the other hand, the sealing portion S is formed of the stepped portion over the relief 202, as shown, in the portion apart from the separate portion 201. In the vicinity of the separate portion 201, however, the sealing portion S is formed at the lower end of the seal ring 200, as shown. At the stepped portion over the relief, as shown, the sealing portion cannot be sufficiently formed to make the sealing properties unstable (as indicated at portion Y).
This results in that the leak also occurs at this portion (i.e., a leaking portion B).
A seal ring 300 having a trapezoidal section is also known, as shown in FIG. 19 to FIG. 22.
This seal ring 300 is given a trapezoidal shape for the sealing portion S of the substantially linear contact so as to reduce the sliding friction. Specifically, the seal ring 300 forms the sealing portion S at the upper end edge of the annular groove 701.
In this case of the seal ring 300, moreover, the sealing portion S is so formed at the upper end edge of the annular groove as to make the substantially linear contact not only in case the side wall face of the annular groove is perpendicular to the groove bottom, as shown in FIG. 19 and FIG. 20, but also in case the side wall face is sloped with respect to the groove bottom, as shown in FIG. 21 and FIG. 22.
In this case of the seal ring 300, a leak occurs through a clearance Z between the projection and the depression in the special step cut no matter whether the side wall face of the annular groove might be inclined or not. The leakage is varied with the slope of the annular groove thereby to raise a problem that the stable leaking characteristics cannot be obtained.
If the side wall face 702a of the annular groove 702 is sloped in the aforementioned case of the seal ring 200, moreover, the sealing portion S is formed of the lower end of the seal ring 200 and the step portion over the relief 202, as shown in FIG. 17, so that a portion (as designated by Y in FIG. 17) of unstable sealing properties is formed.
It is, therefore, conceivable to eliminate the step by forming the relief throughout the circumference, as shown in FIG. 23 and FIG. 24. FIG. 23 is a perspective view showing the mounted state of the seal ring according to a virtual art. FIG. 24 is a schematic section showing the mounted state of the seal ring according to the virtual art.
In the case of this seal ring 400, as shown, a relief 402 is formed throughout the circumference of the ring. Thus, no step is formed in the sealing portion.
Even in case the side wall face 702a of the annular groove 702 is sloped, therefore, only the upper portion of the relief 402 can provide the sealing portion S, as shown, to eliminate the portion of the unstable sealing properties.
In this case of the seal ring 400, however, like the aforementioned case of the seal ring 300 of the trapezoidal section, the leak occurs through the clearance Z between the depression and the projection in a separate portion 401 adopting the special step cut, no matter whether the side wall face of the annular groove might be vertical to or sloped with respect to the groove bottom. With the relief 402 being in the vicinity of the separate portion, moreover, the leakage may become more from that clearance Z.